1. Field of the Invention
The present invention relates to an apparatus which estimates a distance or the like up to a subject by using a range image sensor and two image sensors.
2. Description of the Related Art
There is suggested a method of estimating a plane parameter and a distance according to a gradient method on the basis of luminance information which is acquired from a stereo camera (Refer to Non-patent Document 1: “Lukas-Kanade 20 Years On: A Unifying Framework Part 1: The Quantity Approximated, the Warp Update Rule, and the Gradient Descent Approximation,” S. Baker and I Matthews, International Journal of Computer Vision [2004] Volume: 56, Issue: 3, Pages: 221-255).
There is also suggested a method of estimating a range image by merging a range image acquired by a range image sensor and images acquired by individual stereo cameras (Refer to Non-patent Document 2: “Fusion of Time-of-Flight Depth and Stereo for High Accuracy Depth Maps,” JieJie Zhu, et al. IEEE [2008]).
Specifically, the total likelihood is computed on the basis of the distance likelihood and the luminance likelihood and the distance candidate value having the highest total likelihood among a plurality of distance candidate values is estimated as a distance true value at each pixel of the range image.
The weights of the distance likelihood and the luminance likelihood are determined according to an empirical rule, independently of whether the distance up to a subject is long or short. Accordingly, an influence of the information on a long distance which causes a large measurement error is reflected on the total likelihood to an unignorable degree, by which distance estimation accuracy is likely to decrease.
Therefore, it is an object of the present invention to provide an apparatus capable of improving the estimation accuracy of the subject information including a distance up to a subject.